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A car bomb detonated in the Turkish capital Wednesday near vehicles carrying military personnel, killing at least 28 people and wounding at least 61 others, officials said.

The explosion occurred during evening rush hour in the heart of Ankara, in an area close to parliament and armed forces headquarters. Buses carrying military personnel were targeted while waiting at traffic lights at an intersection, the Turkish military said while condemning the “contemptible and dastardly” attack.

“We believe that those who lost their lives included our military brothers as well as civilians,” Deputy Prime Minister Numan Kurtulmus said.

At least two military vehicles caught fire and dozens of ambulances were sent to the scene. Dark smoke could be seen billowing from a distance.

There was no immediate claim of responsibility, but Kurtulmus pledged that authorities would find those behind the bombing. He said the government had appointed seven prosecutors to investigate the attack, which he described as being “well-planned.”

Kurdish rebels, the Islamic State group and a leftist extremist group have carried out attacks in the country recently. In October, suicide bombings blamed on IS targeted a peace rally outside the main train station in Ankara, killing 102 people in Turkey’s deadliest attack in years.

The deputy prime minister said the violence would not deter Turkey from its fight against terror groups.

“We will never give up on our determination in our fight against terrorism. Whoever is behind this (attack), whoever gave its support, we will find them and bring them to account,” Kurtulmus said.

Wednesday’s attack comes at a tense time when the Turkish government is facing an array of challenges. A fragile peace process with Kurdish rebels collapsed in the summer and renewed fighting has displaced tens of thousands of civilians.

Turkey has also been helping efforts led by the United States to combat the Islamic State group in neighboring Syria, and has faced several deadly bombings in the last year that were blamed on IS.

The Syrian war, meanwhile, is raging along Turkey’s southern border. Recent airstrikes by Russian and Syrian forces have prompted tens of thousands of Syrian refugees to flee to Turkey’s border. Turkey so far has refused to let them in, despite being urged to do so by the United Nations and European nations, but is sending aid to Syrian refugee camps right across the border.

Turkey, which is already home to 2.5 million Syrian refugees, has also been a key focus of European Union efforts to halt the biggest flow of refugees to the continent since World War II. Hundreds, sometimes thousands, of refugees leave every night from Turkey to cross the sea to Greece in smugglers’ boats.

The U.S. ambassador to Turkey, John Bass, said he was “deeply saddened and shocked” by the attack.

“Our hearts and prayers go out to those affected,” he said through his Twitter account.

British Ambassador Richard Moore also offered his condolences through Twitter, writing that the “UK stands shoulder to shoulder with Turkey at this difficult time.”

After the attack, Turkish Prime Minister Ahmet Davutoglu canceled a visit to Brussels Wednesday evening and attended a security meeting with President Recep Tayyip Erdogan and other officials. Erdogan postponed a trip to Azerbaijan planned for Thursday.

The government meanwhile, imposed a gag order which bans media organizations from broadcasting or printing graphic images of the dead or injured from the scene of the explosion. Turkey has imposed similar bans after previous attacks.

Last month, 11 German tourists were killed after a suicide bomber affiliated with the IS detonated a bomb in Istanbul’s historic Sultanahmet district. More than 30 people were killed in a suicide attack in the town of Suruc, near Turkey’s border with Syria, in July.

(AP)